After the captured Justice Leaguers escaped, they contemplated liberating the others. Captain Marvel thought they could use Major Force, as he was a powerful hero. Wonder Woman too felt it would be good to have him. Captain Atom overruled them.
Kylstar's Vessel December 1, 23:58UTC
The Justice League, Superboy, Miss Martian's valiant efforts against Kylstar convinced him to treat his sentient weapons better. All captives, including Major Force, were released, and Orb-One explained Kylstar's motives. He was a freedom fighter who was on a mission to stop slavers who destroyed his homeworld. As a sign of his good intentions, he offered to return captives unwilling to help with his fight back to their homeworlds. Those willing to stay were promised good treatment and glorious battle. Major Force, despite Captain Atom's strenuous objection, chose to remain.
After the others have been teleported away, Kylstar explained to those who remained that the slavers were too powerful, and the best way to defeat them was to take over the galaxy first. Major Force gleefully approved of this course of action.
Major Force was created by the military. He was Supply Sergeant 2nd Class Clifford P. Zmeck, convicted for murder and sentenced to life without parole. A year after the Captain Atom Project, in 1969, he was selected for a second attempt. It succeeded, and the government used him as a hero. Captain Atom was often forced to work beside him, which he did not like.
Known for his savage nature and disdain for women, Major Force was responsible for the (apparent) death of Arisia and the infamous murder of Alexandra DeWitt, Kyle Rayner's girlfriend.